Nano-particles (i.e., particles having average sizes less than about 1 micrometer) are known in the art and are of interest because size and structure dramatically change the properties of the material. For example, the extremely large surface area to weight ratio of nano-particles allows nano-particles to interact with their surroundings very quickly. Nano-particles of pigment material are of particular interest in the inkjet printer industry for use with high-quality printers having many small (e.g., nano-scale) delivery orifices.
Pigment nano-particles can be produced using a primarily mechanical process in which the pigment precursor material is ground in a mill (e.g., a ball mill) until particles of the desired size are produced. Such grinding processes, however, are energy intensive, require substantial amounts of time, and typically result in the production of a powder having undesirable, larger size particles. Such larger size particles must be separated from the pigment nano-particles before use. In addition, the abrasive materials used in such milling and grinding processes may also contaminate the pigment nano-particle material. Consequently, such grinding processes generally are not conducive to the large-scale production of a highly pure pigment nano-particle material.
Consequently, a need remains for a method and apparatus for producing pigment nano-particles that does not suffer from the shortcomings of the prior art methods and apparatus. Such a method and apparatus should be capable of producing large quantities of pigment nano-particle material at low cost. Ideally, such a method and apparatus should be less sensitive to certain process parameters than other systems, thereby allowing the method and apparatus to be more easily practiced on a large scale (i.e., commercial) basis. Additional advantages could be realized if the method and apparatus produced pigment nano-particles in a relatively narrow size range, with a minimum amount of larger sized particles and/or contaminant materials.